This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
You can do it with general file manipulation functions on java.io.File class. However, you should take it a note that attempting to do so makes your web application less portable and less deployable. You can't be certain that you will always have the access to the underneath file system. If you application gets WAR'ed, or if the presence of a security manager prevents access to the file system, your search operation is likely to be failed.
A better way is to rethink why you really need to have such operations to be performed. If you are the one who develops your web application, you should already know the exact file names, so you can fetch them through getResourceAsStream(). If those files are something you are designed to be generated and persisted at the run time of the application, you are probably having a bad architecture.